Lesbian, gay, bisexual, and transgender (LGBT) youth face serious health risks that constitute costly public health concerns. There has been strong documentation of sexual orientation-based disparities on depression, anxiety, and substance use, all of which heighten risk for suicidal ideation and attempts. Further, racial/ethni minority LGBT youth contend with discrimination from multiple marginalized statuses and may face even greater health risks. Yet, there is also a paucity of research on this population. Professional organizations have emphasized the need to consider how social systems contribute to or mitigate health disparities among LGBT populations. Schools are a central access point for resources that may benefit LGBT youth. Few studies, however, have considered school-based programs that address sexual orientation-based health disparities. Gay-Straight Alliances (GSAs) - school-based groups in which LGBT and heterosexual youth receive support and advocate for safer schools - have grown exponentially and serve many youth. Yet, they operate without empirically supported strategies. There are virtually no data on how GSA involvement attenuates negative health outcomes or whether youth from other marginalized backgrounds (e.g., racial/ethnic minority youth, either LGBT or heterosexual) derive benefits. There is a pressing need for data in order to develop effective GSA-based interventions and best practices in general. The current project addresses these gaps. This project is among the first to test how GSA involvement is associated with health outcomes through multiple pathways. It takes advantage of multi-informant data from youth and adults and utilizes quantitative and qualitative data. Data will be gathered from 400 GSA-involved youth (both LGBT and heterosexual) and their GSA advisors among a racially and ethnically diverse sample in 40 GSAs, interviews among 32-40 youth stratified across race/ethnicity, and from a nonmember comparison sample from the same schools. The first aim is to rigorously compare GSA members and nonmembers on health and school outcomes by comparing demographically and socially similar youth in the same school and controlling for confounders. The second aim is to capture variability among GSA members by testing mechanisms by which GSA involvement mitigates negative outcomes. The third aim is to identify race/ethnicity-specific GSA factors that mitigate negative outcomes particularly for racial/ethnic minority youth. Given the growing national presence of GSAs, this knowledge stands to benefit many youth by identifying critical factors underlying health promotion and by providing empirically-based recommendations for best practices to maximize GSA effectiveness. Results will provide a foundation for developing and systematically testing GSA-based interventions.